The present invention relates to a method for impregnating at least one geofabric with a liquid solidifiable polyurethane composition, conforming at least one polyurethane-impregnated geofabric to a surface and allowing the liquid solidifiable polyurethane composition to cure to form a polyurethane/geofabric composite.
The present invention also relates to a method for lining a surface such as a ditch, canal and/or pipe by impregnating at least one geofabric with a liquid solidifiable polyurethane composition, conforming at least one polyurethane-impregnated geofabric to a surface and allowing the liquid solidifiable polyurethane composition to cure to form a polyurethane/geofabric composite.
Liquid solidifiable polyurethane compositions of the present invention have geltimes of from three to twenty minutes, despite changes in application temperature. Such geltimes allow an on-site user sufficient time to apply the polyurethane-impregnated geofabric to a surface before the liquid solidifiable polyurethane composition cures.
Many countries throughout the world place a great deal of importance on the management of natural resources. Water conservation is one important part of managing natural resources.
Losses in the distribution of water due to the use of unlined irrigation ditches are estimated to be, at a minimum, 25% and, in some situations, more than 50%, depending upon the porosity of the ditch surface and the distance the water is moved. In most rural areas, ditches are formed by excavating the soil to a desired depth and width. Water moves through the ditch in contact with the exposed natural surface, i.e., sand, clay, rocks, etc. and. more commonly, mixtures thereof. The porosity of the ditch will not only depend upon the components of the surface of the ditch, but also on the proportion of the different materials present on the surface of the ditch.
The loss of water in unlined irrigation ditches at one time was considered acceptable because water supply exceeded demand. However, as civilization has developed and world population has increased, more water is required for both greater food production and for markedly increasing non-agriculture uses. In addition to greater domestic uses in sanitation, industry now employs large quantities of water in manufacturing and processing procedures.
Although conservation efforts have reduced water consumption to a degree, water is still in relatively short supply. Since cost effective conservation opportunities and readily accessible water supplies have already been developed, attention must be directed to improving the efficiency of water distribution systems.
Some ditches and canals have been lined with concrete and/or preformed concrete pipes, thereby improving the efficiency of these water distribution systems. While concrete is durable and long lasting (if properly used), it is expensive to install and finish. Additionally, concrete can be damaged by unfavorable temperatures during curing, is subject to frost damage, cracking and heaving, all of which can cause water leakage.
Processes for forming composite liners for canals and ditches and apparatuses for performing such processes are disclosed, for example, in U.S. Pat. Nos. 4,872,784; 4,955,759; 4,955,760; 5,049,006; 5,062,740; 5,421,677; 5,607,998; and 5,639,331.
U.S. Pat. No. 5,639,331 (xe2x80x9cthe ""331 patentxe2x80x9d) discloses an apparatus for forming a continuous structure comprising a liquid reactive resin forming material, a particulate solid additive material and a porous blanket. The additive materials are continuously mixed with the liquid resin forming material in an amount significantly greater than that of the liquid resin forming material. Suitable liquid reactive resin forming materials disclosed in the ""331 patent include thermosetting resins such as polyurethanes or polyesters. The apparatus of the ""331 patent comprises multiple reservoirs, one of which can contain an isocyanate, another of which can contain a polyol. The apparatus disclosed in the ""331 patent is used on-site in the fabrication of composite liners for irrigation canals.
The ""331 patent further discloses that resin forming systems may utilize a resin forming material in one reservoir and a catalyst in a second reservoir. However, the ""331 patent does not address the use of catalysts in two component, thermoset polyurethane formulations.
U.S. Pat. No. 5,421,677 (xe2x80x9cthe ""677 patentxe2x80x9d) is directed to an improved process of forming a ditch liner. The mixture of the ""677 patent comprises one or more fillers in an amount up to 60% by weight, based upon the total weight of the mixture. The mixture of the ""677 patent is dispensed on a geotextile, thereby forming a liquid, filler-containing polyurethane soaked geotextile composite. The liquid polyurethane soaked geotextile composite is then placed over the surface of an area to be lined.
The ""677 patent discloses a specific polyol composition comprising at least two different types of polyether polyols to be used in the formulation of the polyurethane/filler mixture. Additionally, the ""677 patent discloses the use of polyurethane catalysts. As shown in the examples of the ""677 patent, a desired amount of catalyst is added to the polyol composition prior to mixing with the isocyanate and filler components. The polyol composition of the ""677 patent is well suited to be used as the liquid, reactive, resin-forming material of the ""331 patent.
Those skilled in the art will recognize that a disadvantage of having a selected constant amount of catalyst contained in the polyol composition (such as is disclosed in the ""677 patent) is that a desired geltime may only be achieved at a given temperature. For example, using an amount of catalyst in a polyol composition such as that disclosed in the ""677 patent will result in a geltime of about ten minutes at 20xc2x0 C. At 50xc2x0 C., the geltime will be less than two minutes, while at 5xc2x0 C. the geltime will be extended to more than thirty minutes.
In order to obtain a certain geltime at a given application temperature, the amount of catalyst would have to be varied according to temperature. This solution, however, would result in multiple polyol compositions containing different amounts of catalyst. This is undesirable not only from an economic point of view, but also from a practical point of view because the polyol component would have to be changed several times within a day when the temperature changes, such as, for example, when the temperature is 5xc2x0 C. in the morning and then 25xc2x0 C. in the afternoon.
Additionally, three-component systems for producing polyurethanes are known. For example, U.S. Pat. No. 6,187,832 (xe2x80x9cthe ""832 patentxe2x80x9d) discloses a process for producing flexible polyurethane foams comprising preparing a rigid foam by feeding three components to a mixing head of a high pressure machine. One component is a polyisocyanate, another component is an isocyanate reactive component containing water and yet another component is another isocyanate reactive component.
The rigid foam of the ""832 patent is prepared by using water as a blowing agent. However, other blowing agents can be used which react with the reactive mixture, thereby liberating a gas which causes the mixture to foam. Subsequently, the rigid foam is crushed to form a flexible foam which is then heated to temperatures between 70xc2x0 C. and 200xc2x0 C.
Although the ""832 patent discloses using two polyol components combined in a mixhead with one polyisocyanate, the process as well as the final product of the ""832 patent are different from the present invention. For example, the ""832 patent discloses preferably using water as a blowing agent which causes the polyurethane composition to foam. Foaming is not desired in a process for producing a non-porous polyurethane/geotextile composite (the process disclosed by the present invention). Also, the two polyol compositions of the ""832 patent have different equivalent weights, whereas the present invention discloses two polyol components having the same equivalent weight.
It is therefore desirable to develop a method for producing polyurethane-impregnated geofabrics wherein the on-site user is able to adjust the amount of isocyanate reactive components in a reactive mixture during temperature changes without changing the ratio of the isocyanate to the sum of the isocyanate reactive components.
The method of the present invention uses three components to form a liquid solidifiable polyurethane composition, i.e., a liquid polyisocyanate component (hereinafter referred to as COMPONENT A); a first isocyanate reactive component which does not contain catalyst (hereinafter referred to as COMPONENT B); and a second isocyanate reactive component which contains catalyst and which has the same equivalent weight as COMPONENT B (hereinafter referred to as COMPONENT C).
COMPONENT B and COMPONENT C are adjusted according to changes in outdoor application temperature. As a result, liquid solidifiable polyurethane compositions of the present invention have geltimes of from three to twenty minutes, despite changes in temperature.
As used herein, the term xe2x80x9cgeofabricxe2x80x9d refers to a geotextile or to a geogrid and/or to a combination of both. xe2x80x9cGeotextilexe2x80x9d refers to any woven or non-woven porous blanket or mat which is produced from natural or synthetic fibers. xe2x80x9cGeogridxe2x80x9d refers to any network of integrally connected polymeric material. Geotextiles are used primarily to line earthen surfaces. Such liners may also be used to line roofs, ponds, reservoirs, landfills, underground storage tanks, canals and ditches.
Examples of geotextiles and geogrids include woven or non-woven polypropylene, polyester, jute and cotton fabrics. Any of the known geotextiles may be used in the present invention.